Some progress with my PDP-11/73 system

[Allison]

>
>Subject: Re: Some progress with my PDP-11/73 system
>   From: David Betz <dbetz at xlisper.com>
>   Date: Tue, 10 Apr 2007 08:17:49 -0400
>     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>
>> RD53s are notoriously unreliable, but I'm surprised that four out  
>> of five simply aren't detected.  Are they genuine DEC RD53s?  You  
>> need to add a PCB link to an ordinary Micropolis 1325 or 1335 drive  
>> to make it an RD53.  Look on the PCB for the location marked R7  
>> (remove two screws and carefully hinge it up) -- if there's nothing  
>> there, solder a link in that position.  Oh, and don't use a skid  
>> plate with bare metal with an RD53, as it can short things out.
>
>Three of the four failing drives were official DEC RD53 drives as  
>indicated by a sticker on the top. Interestingly, when Iooked at R7  
>on the PCB, two of them had the resistor present but one end had been  
>cut. I soldered it back together but both drives still fail. At least  
>one of the drives spins up but then back down again. I'm reluctant to  
>try swapping the PCB between my only working drive and one of the bad  
>ones so I think I'll just count them as a loss.

The one that pinsup and then spins down has the head bumper sticking
problem.  That is repairable and likely the HDA and logic is good.  
Me I'd repair that drive and use it.


Allison